Gundogs are susceptible to a number of different hereditary eye conditions and, as owners, we should be aware of them.
Healthy eyes are a paramount requirement for any working dog. Responsible and proactive breeders play a pivotal role in maintaining eye health in their dogs, and work closely with veterinary eye specialists and geneticists towards this goal. Inherited eye disease can affect any part of the eye – from the eyelids to the lens and the retina. Therefore a basic understanding of eye anatomy is really helpful to understand the various inherited eye conditions.
The anatomy of the eye
The eyeball is made up of three basic layers. The outermost of these layers is divided into the clear window at the front of the eye called the cornea, and the white coat of the eye called the sclera. The cornea in working dogs is prone to wounding by thorns and bushes and is protected by the tear film and the eyelids. In-turning of the eyelids, called ‘entropion’, is painful and can cause scarring and ulceration.
The middle layer of the eyeball is called the uvea and it is this layer that forms the pupil and nourishes the inside of the eye. The lens is suspended by fine fibrils behind the pupil and focuses the in-coming image. If the lens goes opaque, this is called a cataract, which may affect vision depending on its extent.
The innermost layer, called the ‘retina’ is at the back of the eyeball and it is this layer that forms an image and sends it to the brain via the optic nerve. Diseases where the retina stops working result in blindness with an eye that is otherwise normal in appearance.
The unified eye testing scheme
The British Veterinary Association (BVA), the Kennel Club (KC) and the International Sheep Dog Society have teamed up since 1960 to aid breeders in identifying inherited eye conditions in purebred dogs with the BVA/KC/ISDS eye scheme (www.bva.co.uk/Canine-Health-Schemes/Eye-scheme).
The scheme offers eye examination by a highly qualified panel of ophthalmologists throughout the UK for a set fee. This fee is less than the costs for hip and elbow scoring, as well as those for many genetic tests, and it can be reduced further by arranging group testing sessions of more than 25 dogs. Experienced breeders will always have the eye test done first before embarking on the more costly other tests that also might require sedation or anaesthetic. For most breeding stock, eye testing is recommended prior to each time a bitch is bred, whilst frequently used stud dogs should be examined annually. Glaucoma tests are carried out on a less frequent basis and are currently recommended on a three-year basis.
What happens during an eye examination
For the routine eye test, dogs receive a drop of a drug that widens the pupil for a duration of approximately two hours. The drops are applied approximately 30 minutes before the eye test to make sure the pupils are well dilated. The room in which the examination is performed is usually darkened. A combination of a microscope and a bright illuminating lamp called a slit lamp is used to examine the front of the eye and the lens whilst the back of the eye is examined with an ophthalmoscope.
In breeds that are prone to inherited glaucoma, additional tests are carried out before the pupils are dilated. The intraocular pressure may be measured and a small contact lens is applied to the eye after the cornea has been numbed with a drop of local anaesthetic. None of the tests are painful and the most difficult thing can be to keep a wriggly patient sitting still for the duration of the test. Most gundogs are of course so well behaved that it is a pleasure for the panellist to carry out the examination!
Eye tests will always be needed
It’s important to establish that eye examination and genetic testing are never exclusive of each other and should be used in a complimentary manner. Specifically, there are two good reasons why an eye test will never be entirely replaced by genetic testing. Firstly, genetic tests are not yet available for all eye conditions and eye testing is paramount in identifying affected individuals and removing them from breeding programmes in these conditions.
Secondly, the eye examination serves as an early warning by identifying emerging inherited eye conditions. This allows proactive breeders to prevent a disease becoming widely spread throughout the breed before it is officially acknowledged – something which is especially important in numerically small breeds.
What makes a good breeder?
Dogs that have undergone an eye exam under the BVA/KC/ISDS scheme are either certified as ‘clear’ or ‘affected’ for the specific inherited eye conditions identified in their breed. Conditions not yet known to be inherited, and disease of the eyelids, are recorded for future research and for the owners’ information. The UK scheme varies in this from European schemes, where the diseases are not applied as breed-specific. All results of the BVA/KCS/ISDS eye scheme are shared on the Kennel Club website on the ‘Health Test Results Finder’ page. This is really important for transparency and to help breeders plan their programme.
Some breeders have avoided the scheme as they are worried their name might be tarnished if one of their dogs should be affected with a hereditary condition. But any good breeder would know that if you breed long enough, you are eventually bound to encounter a problem even in the best possible line – whether it is eyes, hips, elbows or one of the many other genetic conditions. What makes a good breeder is not never having a dog affected with a hereditary condition, but how they deal with it when it happens. Only this open approach can help us in understanding how conditions are passed on and in finding genetic tests that will eventually eradicate the disease.
The main problems for gundogs
Inherited eye conditions of particular interest for gundog owners are cataract, retinal atrophy, retinal dysplasia and glaucoma. Not all conditions apply to all breeds and information about which disease your dog may be prone to can be found either at the BVA or KC website.
One of the key facts breeders need to know is that very few inherited eye conditions are present at birth (congenital) – most conditions actually set in later in life, with some dogs not affected until they are eight or 10 years old. For a breeder who is looking to establish a successful line, it is thus important not only to have breeding stock examined prior to mating – but also to check their older stock for signs of late-onset inherited eye disease, which has important implications for the offspring they have kept.
The lens is a clear, ellipse-shaped structure behind the pupil that focuses the incoming rays of light onto the retina. Any opacity of the lens is described as a cataract. Many cataracts remain small and never progress to impair vision, whilst others can be rapidly progressive and cause blindness even in young individuals. Inherited forms of cataract are usually defined foremost by their position in the lens and only secondly by their rate of progress.
Gundog breeds currently certified for inherited cataract under the BVA/KC/ISDS scheme include the Irish red and white setter, the large munsterlander, the Chesapeake Bay retriever, the labrador and golden retriever as well as the American cocker and Welsh springer spaniel. Interestingly, these breeds show a similar clinical appearance of their inherited cataract which manifests as an inverted, small Y–shaped opacity at the back of the lens. Some ophthalmologists refer to this type of cataract as the Mercedes Benz sign. This condition is called ‘posterior polar subcapsular cataract’ – or PPC.
It usually is visible in both eyes, although occasionally only one eye is affected – or it may be apparent in one eye before the other. In most affected dogs, the cataract appears some time during adolescence and remains small, not causing an apparent clinical problem. However, in some affected dogs, the cataract can progress and eventually cause impaired vision and blindness. This can be rectified by surgical intervention with cataract removal and lens replacement – which is of course a costly procedure with significant risks.
To date, there has been very limited progress in identifying the genetic cause of most inherited cataracts. A DNA test is not yet available for PPC in the listed breeds. An annual eye examination thus remains the most efficient way to limit the impact of hereditary cataract in gundogs.
Generalised Progressive Retinal Atrophy (PRA)
The retina is the structure that receives the light that has entered the eye through the clear cornea and lens. Here an image is formed by the retinal photoreceptors and the information sent onwards to the area of the brain that is responsible for vision. Many forms of inherited retinal failure (PRA) have been identified with variations in time of onset and speed of progression between different breeds.
For example, Irish setters affected with PRA are born with an abnormal retina which atrophies quickly. As a result, affected setters show clinical signs of the disease within the first months of life and are blind by one year of age. On the other hand, cocker spaniels with retinal atrophy have an initially normal retina, which then starts to fail in the adult dog. Cocker spaniels affected by PRA often do not show signs of vision loss until late adulthood and will retain some sight until aged 10 years or more.
Labradors affected with PRA usually start showing visual impairment quite young – at about four years of age – and may be blind by eight or 10 years. Many dogs affected with PRA will also develop secondary cataracts.
Whatever the genetic variation of PRA, the clinical signs are very similar between most forms. Owners of affected dogs will usually notice impaired vision first at night-time and during times of poor illumination such as dusk and dawn. It is not uncommon to hear affected dogs collide with objects such as dustbins or cars – which are not always in the same place – when walked during early mornings or evenings in winter time. As the condition progresses, the visual deficit becomes apparent during daytime and especially when dogs are exposed to unfamiliar environments. The pupils become increasingly dilated, which results in a greenish reflection similar to that of a cat’s eye at night caught in a headlamp beam. Secondary cataracts are likely to develop also.
Unfortunately, PRA is currently not treatable and affected dogs almost always do eventually go blind. As PRA is mostly a slowly progressive disease, affected dogs are incredibly able to adapt to their visual impairment and function to a level much better than any human, thanks to their superior ears and nose. However, those gundogs relying on sight more than their sense of smell will of course fail to perform well in the field if affected with PRA – the condition usually ends a working dog’s career.
Thanks to collaboration between veterinary ophthalmologists, geneticists and responsible breed clubs, great progress has been made in developing genetic tests for a variety of forms of PRA.
The parable of the Irish red setter
To believe a genetic test could replace a regular screening eye exam would be a fallacy, which has been very well illustrated in the case of PRA in the Irish setter.
The Irish setter was the first dog breed in which a form of PRA was described and researched in detail. Affected dogs were never born with an entirely normal retina, and an experienced veterinary ophthalmologist could identify affected dogs from a very early age. As a result of intensive research, the DNA test for PRA in the Irish setter was the first one to become available commercially. Within a short time, it was believed the disease had been eradicated in the breed and the interest in eye testing diminished.
It was not until older Irish setters were presented as clinical patients and found to be affected with what appeared to be a late-onset form of PRA in the breed that the importance of screening exams became clear again. In due course, a genetic test for late-onset PRA in the Irish setter was developed, but by then 30 per cent of UK Irish setters were believed to be carriers of the disease. A regular screening eye examination for active breeding stock must therefore remain a pillar of any successful and responsible breeding programme.
Retinal Pigment Epithelial Dystrophy (RPED)
This form of retinal degeneration is now rare in the UK but can still occasionally be seen in the spaniel breeds as well as in labradors and golden retrievers. The disease is associated with an abnormal Vitamin E metabolism and diagnosed by the ophthalmologist on account of characteristic brown deposits in the retina. The inheritance of RPED is far more complex than that of the described PRAs due to environmental factors. Clinically, affected dogs present with slowly progressive vision loss and additional neurological deficits can be found especially in the spaniel breeds. It is usually identified in middle-aged dogs.
Retinal Dysplasia (RD)
Retinal dysplasia (RD) describes a failure of the developing retina to unfold evenly on the nourishing tissue at the back of the eye. Two forms of RD are distinguished in the UK – Total Retinal Dysplasia (TRD) and Multifocal Retinal Dysplasia (MRD). In TRD, the retina never fully attaches to the back of the eye and becomes detached in the very young pup – which usually presents blind already to the breeder shortly after opening the eyes. This disease is fortunately extremely rare in the UK.
Multifocal retinal dysplasia (MRD) is more commonly seen in gundogs in the UK, specifically affecting the springer spaniel, the golden retriever and the labrador. In most cases, affected dogs seemingly have normal vision and only an eye examination by a veterinary ophthalmologist will find small areas where the retina is folded. However, in some springers, the condition can be more severe, affecting large areas of retina and causing vision loss and secondary complications such as retinal detachment. A genetic test for MRD is not yet available.
Both MRD and TRD are conditions that can be identified before puppies leave for their permanent homes, and the easiest time to certify puppies as ‘affected’ or ‘unaffected’ is with a litter eye screening exam. In this examination, the entire litter, which must already be permanently identified by microchip, is presented to a panellist for examination between the age of five and 12 weeks. Each puppy will receive a complete eye examination (currently at approximately £11 per puppy) and the relevant findings are noted. This will help breeders to decide which pup is free for MRD and thus is suitable as future breeding stock. As MRD only causes visual impairment in rare cases (which could be identified at the time of the puppy screen), the remaining puppies can be sold in good conscience as working dogs or pets.
This is the most debilitating of all inherited eye diseases, as it not only causes blindness but also severe pain. A cure for inherited glaucoma has not yet been found and whilst many treatments have been developed to delay the devastating effects, almost all affected patients will eventually go blind and may lose one or both eyes.
Glaucoma develops when the pressure within the eye – the intraocular pressure (IOP) – exceeds a certain level. For example, the IOP in most dogs’ eyes normally measures between 10–25mmHg. In glaucoma, the IOP can suddenly increase to levels of more than 80mmHg, which results in acute pain and vision loss due to pressure on the retina and the optic nerve.
Even with rapid intervention, vision may be lost irreversibly within a few hours of such pressure increases. Treatment for glaucoma is life-long once the disease has developed and includes eye drops, tablets and surgeries such as laser-treatment and the implantation of a variety of drainage shunts. All the treatments – even the eye drops – are costly and fail in the long term. Dogs with acute glaucoma are usually in extreme pain and the eyeball becomes swollen, the cornea blue and the white of the eye bright red.
DNA tests to identify dogs affected with glaucoma and those carrying the gene are starting to become available but are currently only limited to a few breeds.
Two forms of glaucoma
The UK’s two forms of inherited glaucoma are primary closed angle glaucoma and primary open angle glaucoma. Fluid to keep the eyeball inflated and nourished is produced by the base of the iris, circulates through the eye and then is drained via a fine perforated sheet of tissue called the ‘pectinate ligament’ into the drainage angle. In primary closed angle glaucoma, the entrance to this drainage angle is occluded by abnormal tissue – termed ‘pectinate ligament anomaly’ (PLA). The degree of PLA can be measured during an eye examination and this can be translated into how likely a dog is to pass a predisposition for glaucoma on to its offspring. At present, the examination cannot identify whether an individual will develop glaucoma in the future, but it can certainly identify ‘at risk’ dogs.
The part of the eye examination to screen for primary closed angle glaucoma is termed ‘gonioscopy’. For this procedure, a contact lens is applied to the eye after the surface of the eye has been numbed with local anaesthetic. The panellist can then examine the pectinate ligament and entrance into the drainage angle.
Currently, four grades (0–3) of PLA are distinguished and only the worst affected dogs (grade 3) are recommended to be removed from breeding programmes. PLA is
a progressive condition and currently it is recommended that gonioscopy is carried out at one year of age and then at three year intervals.
Primary open angle glaucoma (POAG), has also been identified in some working dog breeds, namely the bassett hound and the petit bassett griffon vendeen. Gonioscopy is not helpful in screening for POAG. Instead, other clinical changes identified in the routine eye examination (globe enlargement, changes to cornea and optic nerve head) as well as measurement of the intraocular pressure, are used to diagnose the condition.
Your essential checklist for eye testing
1. Check out which conditions apply to your breed
a. A good place to start is the BVA eye scheme web page (www.bva.co.uk/Canine-Health-Schemes/Eye-scheme) or the KC Assured Breeders Scheme Breed –Specific Health requirements and recommendations web page
b. If your breed does not have a specific known inherited eye disease, it is still a good idea to have a routine eye examination carried out under the BVA/KC/ISDS eye scheme before you breed.
2. Check out which DNA tests you need and which ones your dog might already be hereditarily clear for.
a. For example, if both your dog’s parents have been DNA tested as free for PRA, your dog may be hereditarily clear for this form of PRA so an additional test is not required.
b. This information can be found either on your KC registration document or on the KC health tests results finder web page.
3. Most breeders will present their dog for their first eye test at the age of one – just before any planned hip and elbow x-rays.
a. If your dog is a breed that is prone to glaucoma, gonioscopy can now be carried out for the first time and does not need to be repeated for three years.
b. If your dog tests negative for MRD and TRD, it will be clear for life for these conditions.
c. Hereditary cataract and retinal degeneration can set in years later and regular examination before each time a bitch is bred – or annually in case of a much used stud dog – is necessary to identify these conditions.
d. If you have dogs no longer active in breeding, consider having these examined when they are more than eight years old for a much reduced fee. Findings here will give you valuable information if you have held back offspring of these dogs to continue your line.
e. If you breed litters of breeds that are known to have MRD or TRD, consider having the puppies litter screened before they leave, between 6–12 weeks of age.
Christine Heinrich is the Director of the Eye Veterinary Clinic at Marlbrook near Leominster in Herefordshire.